UNIVERSITY  OF  CALIFORNIA  Agricultural  experiment  Station 

COLLEGE    OF    AGRICULTURE  E.    W.    HILGARD,    DIRECTOR 

BERKELEY,   CALIFORNIA 


CIRCULAR  No.  14. 

(March,  1905.) 


Practical  Suggestions  for  Codling-Moth  Control 
in  the  Pajaro  Valley* 


By    W.    H.    VOLCK. 


The  Codling-Moth.    (Smallest  figure  shows  natural  size.) 

Introductory  Note.— There  were  two  chief  problems  presented  for  solution  in 
the  study  of  the  codling-moth  in  the  Fajaro  Valley,  viz  :  first,  the  frequent  failure 
to  obtain  sufficient  control ;  and  second,  the  very  common  serious  injury  to  foliage 
by  the  material  used.  The  answer  to  the  first  is  that  there  were  too  few  applica- 
tions and  these  not  properly  timed  to  secure  the  best  results.  This  matter  is 
fully  discussed  in  Bulletin  No.  155.  At  the  time  of  the  publication  of  that  bulletin 
the  second  problem  was  not  satisfactorily  answered.  During  the  past  season  and 
the  latter  part  of  the  preceding  year,  Mr.  Volck  has  been  detailed  to  make  a  special 
study  of  this  subject,  and  while  he  is  not  yet  ready  to  give  his  results  in  full,  still 
sufficient  progress  has  been  made  to  justify  definite  recommendations  for  the  com- 
ing season's  work.  While  the  present  circular  is  written  particularly  for  the 
conditions   obtaining   in   the   Pajaro   Valley,   there   is   much   that  may   be  useful   to 


growers  of  apples  and  pears  in  other  sections  where  the  danger  from  burning  the 
foliage  is  small,  in  which  case  paris  green  is  the  most  satisfactory  spraying 
material. 

C.  W.  WOODWORTH. 

In  this  circular  we  will  not  attempt  to  give  technical  details  further 
than  necessary  to  make  intelligible  the  practical  suggestions  herein 
contained. 

The  climatic  conditions  are  such  that,  in  the  greater  part  of  the 
Pajaro  Valley,  paris  green  can  not  be  considered  a  safe  insecticide. 
The  fact  that  it  has  proven  unsafe  in  this  locality  was  a  matter  of 
common  observation  and  experience  with  the  orchardists  of  the  valley 
for  some  years  before  the  Codling-Moth  Investigation  was  undertaken. 
However,  as  much  adulterated  and  poorly-made  paris  green  was  on 
the  market  in  this  State  at  that  time,  the  injury  was  attributed  to  these 
fraudulent  products  and  the  true  cause  was  overlooked.  It  was  with 
this  idea  that  the  investigation  was  undertaken  in  the  spring  of  1903. 

The  object  of  the  early  work  was  to  show  that  the  codling-moth 
could  be  controlled  by  arsenicals  applied  as  a  spray ;  and,  as  the  stand- 
ard arsenical  was  paris  green,  the  greatest  stress  was  laid  on  its  use. 
The  reliability  of  pure  paris  green  was  regarded  as  so  certain  that 
extensive  spraying  operations  were  undertaken  with  it. 

Samples  of  all  the  paris  green  used  in  this  spraying  work  were 
analyzed,  and  no  material  was  applied  which  did  not  come  within  the 
requirements  of  the  State  law  regarding  the  amount  of  free  arsenious 
oxid  and  the  total  arsenic  contained  therein.  Likewise,  the  most 
approved  methods  were  practiced  in  the  preparation  and  application 
of  the  spray. 

With  the  careful  selection  of  material  and  careful  methods  of  appli- 
cation, it  would  seem  that  injuries  resulting  from  errors  or  impurities 
must  be  nearly,  if  not  wholly,  eliminated.  The  marked  injury  which 
was  experienced  in  several  cases  could  not,  therefore,  be  attributed  to 
such  causes,  and  it  naturally  devolved  on  the  investigation  to  deter- 
mine the  factors  productive  of  such  results. 

By  washing  paris  green,  taken  from  a  guaranteed  sample,  for  several 
days,  an  article  practically  free  from  uncombined  arsenious  oxid  was 
obtained.  Plants  treated  with  this  prepared  green  were  injured  quite 
as  rapidly  and  severely  as  those  treated  with  the  unwashed  samples. 
However,  if  the  plants  were  protected  by  cloth  coverings  from  the 
action  of  the  fog  and  dew,  it  was  found  that  no  injury  resulted. 

Such  laboratory  experiments,  together  with  the  results  obtained 
from  the  field  work,  led  to  the  conclusion  that  the  excessive  moisture 
precipitation,  in  the  form  of  fogs  and  dews,  was  the  principal  cause 
of  the   decomposition   and  solution   of   arsenicals,   and,   together  with 


*? 


certain  contributory  conditions,  brought  about  either  the  acute  poison- 
ing of  the  plant  known  as  "burning,"  or  the  chronic  form,  resulting 
in  the  dropping  of  the  leaves.  Among  these  contributory  causes  of 
injury,  the  peculiar  susceptibility  of  the  Yellow  Newtown  Pippin 
variety  of  apple  might  take  first  rank.  Had  these  trees  been  as  resist- 
ant to  arsenical  poisoning  as  many  of  the  other  varieties  found  scat- 
tered through  the  orchards,  little  or  no  trouble  would  have  been 
experienced.  The  Yellow  Newtown  Pippin  is  naturally  delicate,  and 
is  rendered  still  more  so  by  its  susceptibility  to  the  attacks  of  mildew. 
From  these  causes  the  apples  in  a  considerable  portion  of  the  valley  are 
not  more  resistant  to  paris  green  than  peach  trees,  and  even  the 
reduced  doses  recommended  for  use  on  peaches  are  not  wholly  unat- 
tended by  injury  to  the  apple. 

Thus  it  is  apparent  that  the  control  of  the  codling-moth  in  such  a 
locality  is  a  more  difficult  problem  than  is  generally  encountered.  As 
the  amount  of  poison  necessary  to  kill  the  young  larvae  of  the  codling- 
moth  is  relatively  large,  it  became  necessary  either  to  so  treat  the  paris 
green  as  to  render  it  less  affected  by  the  weather,  or  to  discard  it  in 
favor  of  some  more  stable  arsenical. 

Both  of  these  methods  of  preventing  injury  were  followed  out  in 
detail  by  carefully  conducted  experiments.  In  the  first  method  most 
progress  was  made  by  treating  paris  green  with  heavy  oils,  which  in 
combination  with  lime  tended  to  form  a  weather-proof  coating  over 
the  particles  of  the  poison.  The  coating  ultimately  breaks  down,  how- 
ever, under  the  very  severe  conditions  of  the  Pajaro  Valley  and  can 
not  be  considered  a  thorough  success.  The  simple  use  of  large  quan- 
tities of  lime  accomplishes  in  the  end  almost  the  same  result.  This 
expedient  is  practiced  with  success  in  many  apple  regions  and  to  some 
extent  in  the  Pajaro  Valley.  The  search  for  more  stable  compounds 
of  arsenic  met  with  better  success,  for  it  was  soon  found  that  lead 
arsenate  possessed  weather-resisting  properties  to  a  marked  degree. 
Indeed,  the  commercial  brands  were  found  so  resistant  to  weather 
decomposition  that  they  caused  little  or  no  injury  when  used  in  the 
greatest  excess. 

THE    CONTROL    OF    THE    CODLING-MOTH    WITH    LEAD    ARSENATE. 

Having  determined  the  behavior  of  lead  arsenate  toward  foliage,  it 
became  necessary  to  learn  to  what  extent  the  codling-moth  might  be 
controlled  by  it.  Lead  arsenate,  as  an  insecticide,  originated  with  the 
Gypsy  Moth  Commission  in  Massachusetts,  and  it  was  reported  as 
more  effective  than  paris  green  against  the  leaf-eating  larvae  of  the 
gypsy  moth,  possibly  because  a  greater  amount  of  poison   could  be 


__  4  — 

applied  without  injuring  the  foliage.  Thus  the  caterpillars  could  be 
poisoned  by  eating  a  smaller  leaf  surface  than  was  possible  with  paris 
green. 

Eastern  experiment  station  work  also  indicates  that  lead  arsenate  is 
an  efficient  remedy  for  the  codling-moth.  The  results  at  Watsonville 
were  at  first  somewhat  contradictory,  but  it  developed  from  later  work 
that  the  sample  of  lead  arsenate  used  at  that  time  was  not  a  typical 
one.  Later  experiments  indicate  that  a  control  equaling  that  of  the 
best  paris-green  work  might  be  obtained,  but  it  is  equally  true  that, 
weight  for  weight,  the  arsenic  in  paris  green  is  the  most  effective. 
Hence,  in  using  lead  arsenate  a  much  larger  quantity  of  the  poison 
must  be  applied. 

In  the  first  year's  experiments  the  Kedzie  mixture  gave  promise  of 
results,  but,  during  last  season,  the  orchard  treated  most  carefully  the 
year  before  showed  a  greater  amount  of  poisoning  than  was  desirable, 
and  it  is  feared  that  a  continued  use  of  the  mixture  will  result  in  an 
accumulative  effect,  which  may  prove  ultimately  disastrous  to  the 
orchard.  The  unsafe  nature  of  the  Kedzie  mixture  (lime  arsenite) 
was  also  demonstrated  by  numerous  small  experiments  and  by  chemical 
tests  of  leaves  which  had  been  sprayed  according  to  the  standard 
formula.  So  while  very  cheap  and  somewhat  less  injurious  than  paris 
green,  this  mixture  is  not  sufficiently  weather-resistant  to  be  recom- 
mended for  use  in  the  Watsonville  district. 

The  Taft  formula,  which  produces  practically  the  same  results  as 
the  Kedzie  mixture,  being  also  lime  arsenite,  is  another  arsenical 
which  has  given  good  results  in  many  other  sections,  but  will  not 
answer  here  any  better  than  the  former.  Experiments  with  other 
arsenicals  were  still  less  satisfactory,  except  the  lead  compounds  of 
arsenic.  These  come  under  two  principal  groups,  the  arsenites  and 
the  arsenates,  and  of  these  lead  arsenite  was  found  to  be  so  liable  to 
injure  the  plant  that  it  was  never  seriously  considered.  Lead  arsenate, 
on  the  other  hand,  has  proved  the  most  stable  of  all  the  arsenicals.  So 
much  so,  in  fact,  as  to  render  it  safe  at  practically  any  strength. 

The  so-called  home-made  arsenate  of  lead  is  a  compound  produced 
by  combining  a  lead  salt  with  a  salt  of  arsenic  acid,  and  may  be  pre- 
pared by  the  grower  at  the  time  of  use.  In  the  experiments  on  the 
home-made  article  conducted  by  the  investigation,  the  formulas  recog- 
nized by  the  Eastern  experiment  station  were  used,  but  in  no  case  was 
an  article  produced  which  equaled  the  commercial  brands  with  regard 
to  foliage  neutrality.  By  carefully  washing  some  home-made  samples 
in  several  changes  of  water,  an  article  closely  approximating  the  com- 
mercial lead  was  obtained,  but  still  there  was  a  noticeable  difference. 

Some  Yellow  Newtown  Pippin  trees  were  treated  with  home-made 


—  5  — 

lead  arsenate  throughout  the  season  without  injury  to  the  foliage,  but 
as  it  is  desirable  to  use,  for  the  control  of  the  codling-moth,  a  greater 
concentration  than  that  experimented  with,  it  is  hardly  possible  to 
generalize  from  this  test. 

Considerable  difference  was  noticed  in  the  lead  arsenate  samples 
experimented  with,  both  in  their  killing  power  and  in  their  behavior 
toward  foliage.  Of  the  two  commercial  brands,  Disparene  proved  to 
be  the  safest,  as  no  concentration  was  found  which  would  injure  the 
foliage  of  the  most  delicate  plants.  It  was,  however,  less  effective  as 
a  poison  than  the  brand  known  as  Swift's  Arsenate  of  Lead.  The 
maximum  concentration  of  this  arsenate  slightly  injured  peach  foliage 
after  a  considerable  time,  but  this  slight  tendency  to  injure  is  not  con- 
sidered of  any  consequence  in  the  practical  treatment  of  apples  to 
control  the  codling-moth.  The  killing  power  of  Swift's  Arsenate  of 
Lead  was  found  equal  to  that  of  the  home-made  arsenate. 

It  would  then  seem  that  the  Pajaro  Valley  orchardist  is  driven  to 
the  use  of  one  of  the  commercial  brands  of  lead  arsenate  for  immediate 
relief  from  the  codling-moth  next  season.  "Disparene"  is  a  lead 
arsenate  produced  by  the  Bowker  Insecticide  Company  of  New  York. 
According  to  the  analysis  published  in  Bulletin  No.  151  of  the  Califor- 
nia Experiment  Station,  Disparene  was  found  to  contain : 

Per  cent. 

Water  and   volatile   oil 30.00 

Lead   oxid    (PbO) 49.00 

Arsenic   pentoxid    ( AS205) 16.30 

Tar   and   other   organic   matter 4.20 

Total 100.00 

Water-soluble    arsenic    oxid 30 

From  an  analysis  published  in  the  same  bulletin,  Swift's  Arsenate  of 
Lead  was  found  to  contain : 

Per  cent. 

Lead    oxid 36.00 

Arsenic    pentoxid 12.00 

Organic  matter    (Glucose)    and  other  organic  matter 9.00 

Water 43.00 

Total     100.00 

Water-soluble    arsenic    oxid 15 

It  should  be  understood,  however,  that  the  above  statements  of 
ingredients  pertain  only  to  the  samples  analyzed,  and  as  there  is  no 
State  law  controlling  arsenicals  other  than  paris  green,  the  purchaser 
has  only  the  good  faith  of  the  manufacturer  to  depend  on  concerning 
the  uniformity  of  the  product.  He  may,  however,  obtain  more  definite 
information  by  having  samples  out  of  every  lot  purchased,  analyzed 


—  6  — 

by  the  chemist  of  this  Experiment  Station.  As  such  a  procedure 
would  involve  much  delay  to  the  individual  grower,  the  Codling-Moth 
Investigation  is  planning  to  keep  track  of  the  commercial  arsenicals 
on  the  Watsonville  market  during  the  next  season. 

With  the  above-mentioned  difficulty  in  mind  it  is  to  be  deplored  that 
the  manufacture  of  home-made  lead  arsenate  has  not  proven  more 
practical.  Realizing,  however,  that  the  needs  of  the  Pajaro  Valley 
orchardists  are  most  urgent  for  an  insecticide  to  be  used  during  the 
coming  season,  it  is  recommended  that  commercial  arsenate  of  lead  be 
substituted  for  paris  green.  The  experiments  made  last  season  show 
Swift's  Arsenate  of  Lead  to  be  the  most  satisfactory  brand,  and  is 
therefore  recommended,  providing  our  tests  this  season  correspond  to 
those  given  above. 

THE   CONTROL   OF    THE    CODLING-MOTH. 

While  the  selection  of  an  insecticide  adapted  to  these  local  condi- 
tions is  of  prime  importance,  it  is  only  through  the  proper  application 
of  this  insecticide  that  satisfactory  results  are  to  be  obtained.  The 
subject  of  spraying  to  control  the  codling-moth  may  well  be  treated 
under  two  heads:  the  method  of  application  of  the  spray,  and  the 
timing  of  the  applications. 

Methods  of  Spraying.— Our  observations  of  the  methods  of  spraying 
as  the  work  is  actually  done  in  the  Watsonville  district  has  led  us  to 
the  conviction  that  more  thorough  work  is  desirable  in  nearly  every 
case.  As  ordinarily  practiced,  arsenical  spraying  is  of  a  very  super- 
ficial sort.  Practically  all  of  the  spray  is  applied  from  outside.  This 
method  is  thoroughly  satisfactory  for  the  first  spraying,  if  the  whole 
top  of  the  tree  is  treated,  as  it  serves  to  fill  the  blossom  cups  very  well ; 
but  as  the  apples  grow  larger,  an  ever  increasing  amount  of  their  sur- 
face is  not  wet  by  the  spray.  Likewise  the  leaves  which  cluster  about 
the  stem  end  are  not  sufficiently  wetted,  affording  a  protection  for 
young  codling  worms  and  other  Tortricid  larvae,  both  from  the 
weather  and  the  insecticide.  The  large  number  of  late  worms  that 
attack  the  apples  under  such  protection  indicates  the  importance  of 
this  matter.  Indeed,  after  August  the  codling  worm  is  to  some  extent 
migratory,  and  may  inflict  damage  on  several  apples,  always  working 
under  such  protection. 

Thorough  Spraying. — With  these  facts  in  mind  it  will  be  well  to 
give  the  trees  the  benefit  of  thorough  undershot  and  overshot  spray- 
ings, with  the  possible  exception  of  the  first  two  applications.  The 
practice  of  more  thorough  methods  in  spraying  will  not  be  an  innova- 


—  7  — 

tion,  as  in  many  other  sections  where  the  control  of  the  codling-moth 
has  been  an  entire  success  the  apples  are  so  completely  covered  with 
lime  that  it  would  seem  impossible  for  a  worm  to  enter  without  bur- 
rowing through  the  coating. 

The  Timing  and  Number  of  Sprayings.— Throughout  the  Pajaro 
Valley  the  codling-moth  inflicts  the  greatest  damage  during  the  late 
summer  and  fall.  This  fact  has  led  many  to  believe  that  the  late 
sprayings  are  the  most  important,  and  that  the  earlier  ones  might  be 
neglected.  The  fall  infestations  are  due  evidently  to  the  moths  which 
have  developed  from  the  spring  generation  of  worms,  and  the  early 
sprayings  are  to  reduce  the  quantity  of  moths  whose  progeny  make  the 
later  attacks.  There  are  very  few  localities  where  the  spring  and 
early  summer  sprayings  are  not  of  equal  or  greater  importance  in  the 
actual  control-work  than  the  late  sprayings.  The  control  which  may 
be  obtained  through  spraying  is  materially  influenced  by  the  number 
of  eggs  laid,  for  in  any  event  only  a  certain  percentage  of  the  worms 
will  be  killed.  Hence  the  value  of  the  early  sprayings  lies  not  so  much 
in  the  worms  killed  at  the  time,  but  in  reducing  the  number  of  eggs 
to  be  laid  later. 

While  spraying  must  be  practically  continuous,  still  it  is  true  that 
there  are  times  when  little  or  no  egg-laying  is  in  progress.  During 
last  season  such  a  lull  occurred  in  June  and  the  early  part  of  July,  but 
there  was  much  local  variation.  Such  variation  made  it  impossible  to 
outline  any  general  statement  as  to  the  time  of  occurrence  or  duration 
of  the  broods  of  moths.  Again,  the  difference  in  seasons  may  so 
change  these  periods  as  to  make  any  forecast  of  them  absurd.  The 
only  way  in  which  the  lulls  in  egg-laying  may  be  used  to  advantage 
in  reducing  the  expense  of  spraying  is  to  place  breeding-cages,  stocked 
with  pupae,  in  the  orchards  and  observe  the  time  of  emergence  of  the 
moths,  as  was  recommended  in  Bulletin  No.  155  of  this  Station.  This 
is  not  too  difficult  a  matter  for  the  average  grower  to  undertake,  but 
we  do  not  expect  that  many  will  adopt  it  before  the  saving  effect  has 
been  demonstrated  in  a  number  of  orchards.  To  make  such  demon- 
strations will  be  a  very  important  part  of  the  work  of  the  Codling- 
Moth  Investigation  during  the  next  season. 

In  the  meantime,  when  the  periods  of  egg-laying  are  not  accurately 
known,  the  only  safe  way  is  to  assume  that  the  orchard  needs  spray- 
ing at  regular  intervals  from  the  falling  of  the  blossoms  to  the  pick- 
ing of  the  fruit.  The  intervals  between  sprayings  should  not  be  too 
great,  for  while  the  leaves  hold  the  poison  very  tenaciously,  and  tend 
to  accumulate  a  larger  amount  as  the  season  advances,  the  fruit  is 
subject  to  loss  through  its  rapid  growth  and  the  consequent  scaling  off 


—  8  — 

of  the  arsenical.  Also,  the  growth  of  the  apple  develops  a  new  sur- 
face which  must  be  covered  with  poison.  All  things  considered,  the 
time  between  sprayings  need  not  be  materially  less  than  three  weeks, 
and  should  not  be  greater  than  one  month. 

The  following  programme  applies  to  the  Pajaro  Valley: 

The  First  Spraying.— -The  first  spraying  with  arsenate  of  lead  should 
be  applied  as  soon  as  the  first  blossoms  have  fallen.  Owing  to  the 
variations  in  seasons  it  is  not  possible  to  fix  an  exact  date,  but  this 
will  be  about  April  10th.  Do  not  wait  for  all  the  blossoms  to  fall,  as 
this  may  delay  the  operation  until  the  blossom  ends  of  the  majority  of 
the  young  apples  have  closed.  At  this  spraying  the  use  of  a  large 
amount  of  material  will  be  advisable,  i.  e.,  3  pounds  to  50  gallons  of 
water.  Fear  of  rains  need  not  delay  the  operation,  as  lead  arsenate 
sticks  much  better  to  the  foliage  than  paris  green  and  there  is  no  danger 
from  water-soluble  arsenic* 

The  Second  Spraying.— About  the  30th  of  April  the  orchard  should 
receive  another  spraying.  At  this  application  spray  thoroughly  both 
upper  and  under  side  of  the  leaves,  but  with  as  little  drip  as  possible. 
Use  2  pounds  of  lead  arsenate  to  50  gallons  of  water. 

The  Third  Spraying.— This  spraying  should  be  applied  about  the 
17th  of  May.  A  concentration  of  1%  pounds  of  lead  arsenate  to  50 
gallons  of  water  should  be  sufficient.     The  spraying  should  include 

*  While  lead  arsenate  is  a  very  great  improvement  over  paris  green  in  the  matter 
of  retention  or  rain  resistance,  it  may  be  improved  in  this  respect  by  adding  some 
adhesive.  The  resin-soap  adhesive  has  given  excellent  results  in  the  East.  It  is 
prepared  according  to  the  following  formula  : 

Pulverized    resin 5  pounds. 

Concentrated    lye 1  pound. 

Fish,  or  other  animal  oil   (except  tallow) 1  pint. 

Water    5  gallons. 

Place  the  oil,  resin,  and  one  gallon  of  hot  water  in  an  iron  kettle  and  heat  until 
the  resin  softens ;  then  add  the  lye,  and  stir  thoroughly ;  now  add  four  gallons  of 
hot  water,  and  boil  until  a  little  will  mix  with  cold  water  and  give  a  clear  amber- 
colored  liquid ;  add  water  to  make  up  five  gallons ;  keep  this  as  a  stock  solution, 
and  for  use  take  one  gallon  of  stock  solution  to  twenty-five  gallons  of  arsenate  of 
lead  spray  mixture. 

The  flour-paste  adhesive  so  successful  in  causing  the  sulfur,  used  in  sulfur  spray- 
ing for  red  spiders  (Bulletin  No.  154,  California  Experiment  Station)  to  resist 
the  action  of  the  rain,  will  also  answer  well  here.  It  is  prepared  as  follows :  Take 
one  pound  of  wheat  flour  to  one  gallon  of  water.  Place  the  flour  in  a  box  with  a 
screen  bottom  (common  wire  window  screening),  and  pour  the  water  through  it 
until  all  the  flour  has  been  washed  into  the  receiving  vessel.  It  will  then  be  finely 
divided  and  free  from  lumps.  The  mixture  should  then  be  brought  to  the  boiling 
point,  being  stirred  constantly,  thus  forming  a  thin  paste  without  lumps.  Use  four 
gallons  of  this  paste  to  every  one  hundred  gallons  of  water;  run  it  through  a 
strainer  before  adding  to  the  spray  mixture. 


a  vi 


—  9  — 

thorough  overshot  and  undershot  applications.  A  special  effort  to  wet 
the  stem  ends  of  the  apples  on  the  inside  of  the  tree  will  doubtless 
prove  beneficial. 

The  Fourth  Spraying.— A.  reasonable  interval  would  place  this 
application  about  June  17th,  and  the  arsenate  of  lead  may  be  reduced 
to  a  minimum,  or  1  pound  to  50  gallons  of  water. 

The  Fifth  Spraying.— About  July  10th  another  spraying  will  be 
advisable,  using  1  pound  of  lead  arsenate  to  50  gallons  of  water. 
This  time  considerable  care  should  be  taken  to  spray  the  inside  of  the 
tree  and  also  to  reach  the  stem  ends  of  the  apples. 

The  Sixth  Spraying.— On  August  1st  the  sixth  application  should 
be  made  as  directed  for  the  fifth. 

The  Seventh  Spraying.— Another  application  is  due  about  the  21st 
of  August.  As  the  later  and  more  severe  attack  of  worms  is  now 
becoming  evident,  the  material  should  be  increased,  using  about  2 
pounds  to  50  gallons  of  water.  At  this  time  great  stress  must  be 
placed  in  wetting  the  stem  ends  of  the  apples  under  the  leaf  protec- 
tions. The  entire  under  surface  of  the  fruit  also  needs  wetting;  this 
can  only  be  accomplished  by  undershot  spraying. 

The  Eighth  Spraying.— On  or  about  September  12th  another  appli- 
cation as  directed  for  the  seventh  spraying  should  be  made. 

The  Ninth  Spraying.— During  the  first  week  in  October  another 
spraying  should  be  given,  using  2  pounds  of  lead  arsenate  to  50  gal- 
lons of  water.  This  application  should  be  followed  by  other  sprayings 
every  three  weeks  until  the  fruit  is  picked. 

Results  to  be  Expected  from  Spraying.— The  great  drawback  which 
has  militated  against  the  complete  success  of  spraying  in  the  Pajaro 
Valley  was  the  injuries  to  the  trees  from  paris  green  and  other  arsen- 
icals.  These  injuries  made  it  necessary  in  most  cases  to  abandon  active 
spraying  operations  just  at  a  time  when  the  campaign  should  have 
been  most  energetically  prosecuted. 

The  adoption  of  a  safe  insecticide  will  remove  this  difficulty,  so  that 
results  comparable  with  those  obtained  elsewhere  may  confidently  be 
expected.  It  should  be  remembered  in  this  connection  that  even  when 
spraying  was  abandoned  about  the  middle  of  August,  1903,  a  control 
of  95  per  cent  was  obtained  in  many  orchards.  Then  conscientious 
work  with  lead  arsenate  may  be  expected  to  yield  a  control  in  the 
neighborhood  of  95  to  98  per  cent. 

The  Cost  of  Spraying.— Arsenate  of  lead  spraying,  figuring  on  the 
commercial  lead  at  15  cents  per  pound,  will  be  nearly  twice  as  expen- 
sive as  paris  green  for  the  same  sized  tree. 


—  10  — 

For  the  schedule  just  given,  the  lead  for  nine  sprayings  will  cost 
$2.10.  This  is  to  be  diluted  with  450  gallons  of  water  and  applied  at 
the  rate  of  five  gallons  per  tree  per  application  (the  estimate  is  made 
for  a  full-bearing  orchard) ,  or  forty-five  gallons  for  the  nine  sprayings. 
This  gives  21  cents  as  the  cost  of  material  per  tree,,  and  a  fair  estimate 
of  the  cost  of  application  per  gallon  would  be  about  one-quarter  of  a 
cent,  which  makes  a  total  cost  of  32  cents.  This  figure  looks  large,  but 
it  is  desired  to  give  an  over,  rather  than  an  under  estimate  in  making 
an  approximate.  Even  considering  the  cost  of  35  cents  for  the  larger 
full-bearing  trees,  it  is  not  more  than  half  the  net  returns  on  a  box  of 
sound  apples.  So  if  the  control  expected  is  obtained,  spraying  at  this 
figure  will  prove  a  very  profitable  investment. 

Objections  to  Arsenical  Spraying.— In  every  section  where  arsen- 
ical spraying  for  the  codling-moth  is  practiced,  the  solid  deposit  left 
on  the  fruit  probably  gives  rise  to  more  or  less  criticism,  but  in  practice 
this  has  not  proved  objectionable. 

In  other  apple-growing  sections  this  whitewash  is  carried  to  such 
an  extent  that  the  color  of  the  fruit  is  obscured,  but  when  the  coating 
is  wiped  off  the  rind  is  found  in  as  good,  if  not  in  a  better,  condition 
than  that  of  the  unsprayed  product. 

The  poisonous  effects  of  the  arsenicals  on  persons  eating  the  sprayed 
fruit  while  applying  the  wash  might  be  imagined  to  be  a  serious  objec- 
tion to  their  use.  In  fact,  however,  no  authentic  case  of  poisoning  has 
developed,  and  it  may  be  further  stated  in  this  connection  that  minute 
quantities  of  arsenic  have  been  proved  to  be  harmless  and  are  always 
to  be  found  in  the  system. 

With  regard  to  the  dangers  arising  from  the  application  of  the 
spray,  this  injury  is  least  with  good  commercial  lead  arsenate  because 
of  its  complete  insolubility,  which  renders  it  impossible  for  the  opera- 
tors to  absorb  any  poison  through  the  pores  of  the  skin.  The  manu- 
facture of  home-made  lead  arsenate  might  subject  those  in  charge  of 
that  part  of  the  operations  to  the  danger  of  lead  poisoning,  but  it  is 
hardly  probable  that  any  one  would  remain  at  this  work  long  enough 
to  be  affected. 

SUMMARY. 

It  is  recommended  that  paris  green  be  discarded  in  all  localities 
where  its  careful  use  has  proved  injurious  to  the  trees. 

Arsenate  of  lead  has  been  found  reliable  as  an  insecticide  as  well  as 
neutral  toward  vegetation,  and  its  use  is  recommended. 

During  the  coming  season  the  growers  are  advised  to  use  commercial 
lead  arsenate,  rather  than  attempt  the  production  of  the  home-made 
article. 


—  11  — 

Eight  to  ten  sprayings  are  recommended  to  be  applied,  as  indicated 
the  table  below: 


Amount  of  Material 

to  ITsfi. 

Number  of 

Approximate 

Date  of 
Spraying. 

Method  of  Application. 

Application. 

Arsenate  of 
Lead. 

Water. 

1st 

April  10 

3  lbs. 

50  gals. 

Overshot. 

2d 

April  30 

2  lbs. 

50  gals. 

Over-  and  undershot. 

3d 

May  17 

li  lbs. 

50  gals. 

Over-  and    undershot;    thor- 
ough inside  spraying. 
Over-  and    undershot ;    thor- 

4th 

June  12 

lib. 

50  gals. 

ough  inside  spraying. 
Over-  and    undershot;    thor- 

5th 

July    10 

lib. 

50  gals. 

ough  inside  spraying. 
Over-    and    undershot;     very 

6th 

Aug.     1 

lib. 

50  gals. 

thorough  inside  spraying. 

7th 

Aug.  21 

2  lbs. 

50  gals. 

Over-    and    undershot;     very 
thorough  inside  spraying. 

8th 

Sept.  12 

2  lbs. 

50  gals. 

Over-    and    undershot;    very 

thorough  inside  spraying. 
Over-    and    undershot;    very 

9th 

Oct.       1 

2  lbs. 

50  gals. 

thorough  inside  spraying. 

Subsequent  spray 

ing:    every 
ruit  is  picked. 

1  to  2  lbs. 

50  gals. 

Over-    and    undershot;     very 

three  weeks  until" f 

thorough  inside  spraying. 

